The presses used in the domain of moulding are usually actuated by a piston which moves either under the action of a hydraulic fluid under pressure, so that the pressure of injection exerted on the material to be moulded is a function of the hydraulic pressure exerted upstream of the piston of the press, or under the action of a force generated by mechanical or electrical means.
Furthermore, it is known that numerous parameters influence the value of the pressure applied to the material inside the mould. In practice, the presses of the prior state of the art comprise means for controlling the hydraulic pressure applied to the piston and means for measuring the pressure of the material inside the mould where the injection is effected. It is also known that, in stable operating conditions of the injection press, by simply regulating the pressure of the hydraulic fluid, the pressure of the material inside the mould can thus be maintained within a range, satisfactory in certain cases, despite the influence of all the technical parameters which have influence thereon, particularly the operating parameters of the machine.
Such constant and regular operating conditions of the injection press are maintained as long as no noteworthy disturbance occurs. Among the disturbances that may modify the operating conditions of the press may be retained, in particular, the stoppages thereof, whether they be necessary for normal operation of the machine or whether they be accidental, as well as the influence exerted by the variations in temperature or the irregularity of the material itself if a recycled material is used. When such disturbances occur during a cycle of injection, it is known that it is necessary to make the installation operate thereafter for a more or less long period of time, which depends on the characteristics of the press and the material to be moulded, before resuming new stable operating conditions. Moreover, the level of these new stable operating conditions may be very different from the earlier level of stability, which is translated by very different characteristics of moulded products.
During the operating time of the press under disturbed conditions, a certain number of pieces are, of course, produced which, for the majority, do not fulfill the specifications imposed, particularly concerning their mass and/or their dimensions, with the result that such pieces are discarded, which represents both a loss of time and of money.